There are three issues here:
- People most often lie for a reason. Your boyfriend is telling alot of lies, which I would see as an immedite warning sign that there are deeper issues at play in his mind. The lies are just the forward shield he puts fourth to hide or divert others - including you - away from the truth.
- People often won't admit they have a problem and ask for help until they hit a point of realization that there really is something wrong with their behavior. Your boyfriend hasn't had that realization yet.
- People often think they can "fix" other people. I'm sure you think that is you can help him and get him to change... but it's much more likely that you can't, and the pattern of behaviour will decline further over time.
If you stay with him, be prepared to have alot of patience and understanding with his constant lies. Maybe you can take that, after all you've been with him for three years already.
I'd suggest making a choice that is healthy for you. I think that it's only a short hop from being a liar to being untrustworthy. I fit were me, and I saw he was one that "lies for everything", I would be gone before the next lie comes out of his mouth.